A SYNOPSIS OF THE SPECIES OF ISOETES. 67 



4. I. lacustris, Linn. ; Hook. Brit. Ferns, t. 55 ; Duriou, Bull. 

 Bot. France, 1861, 164; A. Br. in Verb. Branden, 1862, 17.— I. 

 atrovirens, T. Fries.— I. macrospora, Durieu. — J. Morei, D. Moore. 

 Bootstock 2-lobed, generally about £ in. diam. Leaves generally 

 20-505 8-6 in. long, £-1 lin. diam. at the middle, dark green, 

 flaccid, diaphanous, tapering to the point, the edge decurrent from 

 the base short and narrow, without stomata or accessory bast- 

 bundles. Sporangia subglobose or oblong, |~£ in. long, 

 unspotted; veil partial. Microspores large, white, strongly 

 granulated. Microspores quite smooth. 



Hab. Widely spread in the lakes of Northern and the 

 mountains of Central Europe ; rare in North America. Durieu, 

 m Bull. Bot. Soc. France, xi. 102, separates the American plant 

 by its larger macrospores as a species as L macrospora. I. Morei, D. 

 Moore in Journ. Bot., 1878, 353, t. 199, from Lough Bray, 

 Wicklow, is a large flaccid form with leaves about a foot long. 

 I. crassa, setacea, and tenella of Leman and Desvaux represent 

 three forms of this species as to robustness of growth. ' 



5. I. eohinospora, Durieu in Bull. Soc. Bot. France, viii. 164 ; ^ y{ 

 A. Br. in Verb. Brand., 1862, 24 ; Bab. in Journ. Bot., 1863, 



t. 1.— Rootstock f-f in diam., 2-lobed, rarely 3-lobed. Habit of 

 I. lacustris, but leaves more slender, generally 20-50, 4-6 in. long, 

 about | lin. broad at middle, flexible, diaphanous, light green, 

 tapering gradually to the point, the edge decurrent from the 

 dilated base narrow and short. Sporange globose or oblong, J in. 

 long, unspotted ; veil short. Macrospores middle-sized, distinctly 

 spinulose all over. Microspores slightly papillose. 



Hab. The type widely spread in the lakes of Northern and 

 Central Europe, often associated with /. lacustris. In /. Braunii, 

 Uurieu (I. ambigua, A. Br.), of North America, Greenland, and 

 Iceland, the leaves are darker green, with a few stomata, the 

 veil larger, the sporange spotted, and the microspores smooth. In 

 • mur icata, Durieu, of New England, the leaves are longer, the 

 unspotted sporange half covered by the veil, and the spinules of 

 the macrospore shorter; and in J. Boottii, A. Br., of Boston, 

 U.b.A., the leaves are stiffly erect, with a few stomata, and the 

 macrospores rather smaller, with very slender spinules. 



2 1 h I,AZ0RIC . A » I)urieu ; Milde Fil. Eur., 278.— Bootstock probably 

 jMobed. Habit of I. echinospora. Leaves 2-3 in. long, under \ lin. 

 broad at the middle, light green, diaphanous, without stomata 

 j* accessory bast-bundles. Sporangia subglobose, unspotted, 1-1 £ 

 m \ *® n gl veil large, but partial. Macrospores middle-sized, 

 reticulated over both halves. Microspores granulated. 

 iv Azores, in a shallow pool in the island of Corvo, H. C. 



watson, 349 ; a few specimens collected in the year 1842. 



2 1 k }' PYGMiEA > Engelm. in Amer. Nat., 1874, 214.— Kootstock 



to ?1 • Lea T es 5 ~~ 10 > i- 1 in - lon g> dark green, tapering rapidly 



tiie point, without stomata or accessory bast-bundles. Sporange 



gobose; veil very narrow. Macrospores middle-sized, marked 



